• State TI Thinks Resolved
  • Locked Locked
  • Replies 4 replies
  • Answers 2 answers
  • Subscribers 21 subscribers
  • Views 217 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TXB0104: Pull res, cap limitation is only for output drivers?

DELJO DAVIS
Intellectual 270 points
Part Number: TXB0104
Other Parts Discussed in Thread: TXU0304, TXU0104, TXU0204

Tool/software:

HI Team,

In the TXB0104RUT datasheet i saw below

I hope the 70pf capacitance and 50K pull resistor limit only apply for the output  pins of TXB0104RUT  and not to the TXB0104RUT pins which are input/receivers to external signals

For ex in my case my host processor is output and TXB0104 is input. and i have 300pf capacitance and 20K pull resistors between processor and TXB0104RUT.  Is this an issue?

 

  • 0
    Guru 317250 points

    The TXB is bidirectional; all I/O pins are inputs and outputs at the same time.

    If your signals are not actually bidirectional and a pin is always an input pin, you can use resistors and a higher capacitive load. But then the TXU0104/TXU0204/TXU0304 would be a better solution.

  • 0
    TI__Mastermind 40976 points

    Hi Deljo,

    Clemens' is correct here- you may also refer to Overcoming TXB-Type Translator Design Challenges for design considerations with the TXB. Please let us know if you have any additional questions. 

  • 0 in reply to Jack Guan
    Intellectual 270 points

    HI Clemen,

    See my below schematic diagram

    TXB 10,9,8,7 pins connected to a host processor.  and this host Processor pin is always output . So TXB 10,9,8,7 should be always input.

    And i have 300pf capacitance and 20K pull up/down resistors on the host processor side. So you saying since the pull resistor, cap on the input side of TXB no issues. right?

    Any reason why you recommended TXU0104/TXU0204/TXU0304 ?

  • 0 in reply to DELJO DAVIS
    Guru 317250 points

    UART RX/TX pins usually go in opposite directions. Are you sure that all these signals are output by the host processor?

    The TXB has a very low drive strength to allow bidirectional signals. For unidirectional signals, high-impedance inputs and strong outputs (like with the TXU translators) are easier to use and more robust.